It's an equal opportunity crime -- there are folks of all backgrounds who are trashing our public lands. Being opposed to illegal use of the land does not necessarily imply any sort of political bias. I am disturbed by left wing graffiti artists at Joshua Tree, right wing Cliven Bundy fans tearing up cryptobiotic soil in Utah, cartel-affiliated marijuana growers in the Sierras, apolitical boondockers who scatter garbage around, gun enthusiasts who shoot up the landscape and leave their spent brass, game poachers, you name it.
The question is what to do about it when you see it, and the answer is easy -- contact the appropriate law enforcement agency and do not try to solve the problem yourself. Lots of these folks are armed.